1. Field of the Invention
The present invention relates to three-port valves, and in particular to a three-port valve having a fluid inlet and first and second fluid outlets.
2. Description of the Related Art
Three-port valves are devices that make it possible to control the flow of a fluid, which may be a liquid or a gas, and they are used in a wide variety of fluid flow systems. Among systems that make use of three-port valves, there can be found, for example, the attitude and roll control systems for space vehicles, launchers, or rockets, in which said three-port valves are used for controlling the flow of gas to propulsive nozzles, or to systems for feeding propellant to propulsive thrusters of such vehicles.
Thus, in attitude and roll control systems for stages of the Ariane 5 launcher, a three-port valve is known that comprises a casing having a fluid inlet and first and second fluid outlets, together with an element that is movable in the casing. In that three-port valve, the movable element comprises a rod, a first valve member fastened to a first end of the rod, and a second valve member fastened to a second end of the rod. The first valve member is suitable for being received, towards the rod, in a first valve seat in order to close a first fluid-flow passage between the fluid inlet and the first fluid outlet, and the second valve member is suitable for being received, towards the rod, in a second valve seat in order to close a second passage between the first and second fluid outlets. The length of the rod allows the movable element to move between a first position in which the first passage is closed and the second passage is open, and a second position in which the first passage is open and the second passage is closed. Thus, in the first position, the inlet is shut off and pressure between the two outlets is equalized, whereas in the second position the valve enables fluid to flow from the inlet to the first outlet, while isolating the second outlet.
Such valves may be subjected to extreme levels of stress, in particular vibratory stress. A problem that can then arise is the valve members moving off-center relative to the corresponding valve seats, as a result of the rod moving radially or tilting relative to the casing. Such off-centering can lead to the valve members and/or the valve seats being damaged during movements of the movable element, and can also lead to the movements of the valve being slowed down or even jammed. Unfortunately, the ability to withstand vibratory environments and also the response speed and the reliability of a valve are fundamental factors in such applications.
In the prior art, attempts have been made to solve that problem by guiding the rod through a narrow bore in the casing. Unfortunately, that solution leads to a certain amount of friction and thus likewise to the valve being slowed down and running the risk of jamming.